Apparatus for making aluminum nitride and other chemical substances



V w. HOOPES. APPARATUS FOR MAKING ALUMINUM NITRIDE AND OTHER CHEMICAL SUBSTANCES.

APPLlCATION FILED SEPT. 19, 1919.

Patented May 9, 1922.

5 SHEETS-SHEET I.

Invenior: Wz/ui/amHoo'pes, b I 7 w ags.

W. HOOPES.

APPARATUS FOR MAKING ALUMINUM NITRIDEAND'0THER CHEMI CAL SUBSTANCES.

APPLICATION FlLED SEPT. 19, 1919.

Patented May 9, 1922 5 suns-sum 2.

Invenior Wi/ZZZJLIZQH OOP as,

w. HOOPES. APPARATUS FOR MAKI LUMINUM NITRIDE AND OTHER CHEMICAL SUBSTANCES.

PPLICATION FILED SEPT-19,- l9l9.

1,415,446. atente ay9,-1922.

Imenior Zi/amHoopes,

w. HOOPES.

APPARATUS FOR MAKING ALUMINUM NITRIDE AND OTHER CHEMICAL SUBSTANCES. APPLICATION ED'SEPT 19 1919 Patented May9,1922.' 5 EEEEEEEEEEEE 4.

Inveni'or 4 miliamfloppem W. HOOPES. v APPARATUS FOR MAKING ALUMINUM NITRIDE AND OTHER CHEMICAL SUBSTANCES.

APPLICATION FILEDSEPT. 19, 1919.

1,415,446. I Patentd May 9, 1922.v

Iii/0827,31)? T ViZZiamHo op es,

Y Allegheny and State of 0mm s rArss PATENT. optics.

WILLIAM HOOPES, 01K PITTSBURGH, PENNSYLVANIA, ASSIGNOR T0 ALUMINUM COMPANY OF AMERICA, 0]! PITTSBURGH, PENNSYLVANIA, A CORPORATION OF PENNSYLVANIA.

APPARATUS FOR MAKING ALUMINUM NITRIDE AND OTIE IER CHEMICAL SUBSTANCES.

Specification of Letters Patent. Pa tented May 9, 1922.

Application filedv September-19, 1919. Serial No. 324,7 83.

To all whom it may concern:

Be it known that I, \VILLIAM Hoo'rns, a citizen ofthe United States of America, and a resident of Pittsburgh in the county of l ennsylvania, have invented an Improvement in Apparatus for Making Aluminum Nitride and Other Chemical Substances, of which the following description, in connection with the accompanying drawings, is a specification, like characters on the drawings representing like parts. 4

This invention relates to apparatus or means for practising processes involving chemical reactions, and more particularly to those involving chemical reactions between solid and gaseous bodies.

In practising processes of the general character descr1bed,.the solid bodies thatare to take part in the reaction are usually mixed to form a charge, and the gas is caused to act upon the latter.

In proceeding in this manner I have found that in order successfully to practise processes of this kind it is necessary to realize certain conditions, particularly if the process is to prove a commercial success. One of these conditions is that the bodies both solid and gaseous, which are to take part in the reaction, shall all come into intimate contact with each other throughout the entire charge, and to this end it is necessary that the. bodies both solid and gaseous be as evenly distributed as practicable throughout thellatter. Furtherm'ore,'where heat is absorbed in the reaction, another condition is that the heat be supplied or distributed at the reaction temperature throughout the mass and that the mass be maintained at the requisite temperature during the reaction. In order to realize-these conditions the solid materials forming the charge should be processes Which otherwise would-have proved acommercial success.

One of the objects of my invention is to provide apparatus or means realizing the conditions above set forth. Other objects of my invention will be in part obvious and in, part pointed out hereinafter.

' My invention and its aims and objects will be best understood from the following description taken in, connection with the accompanying drawings of one illustrative form of apparatus or means embodying my invention, the scope of the invention being more particularly pointed out in the ap--- pendedclaims.

In the drawings Fig. 1 is a front elevation of one illusplan view of the apparatus- 'trative form of apparatus or means embody- 5-5 of Fig. 1, certain parts being shown in elevation.

I will now describe one illustrative form of apparatus or means embodying my in vention, in its application to the production of a specific substance, more particularly aluminum nitride. It is to be understood, however, that my invention is not limited to the production of this substance, but that as to its general features and also as to certain of its more specific features as well, it is equally applicable to the production of other substances, including other nitrides.

In the illustrative form of my invention herein shown, 2 designates the: walls of a preferable circular shaft furnace, said walls being constructed of any suitable material, such as fire-brick, silica, magnesite, bauxite, or the like, capable of resisting high temperatures. The bottom wall 4 of the furnace,

is provided with an annular space 6 whichis preferably covered by a grate 8; Suitable means is provided to conduct a nitrogencontaining gas into the furnace. In the illustrative embodiment of the invention herem shown such means comprises a plurality of pipes 10 extending radially through the lateral walls 2- 0f the furnace beneath the grate 8, their inner ends opening into the annular space 6 and their outer ends being connected with a common supply pipe 12 extending about the lower part of the furnace, and itself connected to a larger supply pipe 14 leading to any suitable source of supply, not shown, of nitrogen or nitrogen-containing gas. Herein six pipes 10 are provided, but the number may vary according to the size of the furnace. Through these pipes 10 the nitrogen or nitrogen-containing gas to be used in the reaction is introduced into the furnace.

While I may use any source of heat in accordance with my invention, 1 preferably use electrical energy for this purpose, proceeding preferably on the resistance principle of heating, the charge forming a conducting path between suitable electrodes connected to any suitable electricity supply. The heat is thus developed with practical uniformity throughout the cross-section of the charge, a condition required for the maintenance of uniform temperature while performing the reaction. The use of arcs adjacent the charge for developing the heat,

or even of arcs where the charge constitutes one terminal of the arc, has proven unsatisfactory, as the major portion of the heat is developed in the arc with the production of local high temperature at that point instead of uniform temperature throughout the entire charge. The same thing in a lesser degree applies tothe development of the heat by means of resistors placed external to the charge. In that case the'resistors must run at a higher temperature than is maintained within the charge, and the portions of the charge adjacent the resistors are heated to higher temperatures than those portions of the charge further removed from the resistors, with the result that, if the portion-of the charge adjacent the source of the heat are at the proper temperature for the reaction, those portions of the charge further removed from the source of heat are at too low a temperature for the reaction, or conversely, if the portions of the charge far removed from the source of the heat are maintained at the proper temperature for. the reaction, then those portions of the charge adjacent the source of heat are overheated with resulting volatilization or fusion of the mass.

To the above end I provide a plurality of electrodes 16 extending horizontally through the lateral walls 2 of the furnace, near the bottom of the latter but above the grate 8, while above the furnace there are suspended in any suitable manner a plurality of vertically disposed electrodes 18. All of these electrodes will'preferably be of carbon, eight lower electrodes 16 and thirteen upper electrodes 18 being herein provided, but the number of electrodes used will vary according tothe size of the furnace used, it being to distribute the current through the fun nace. The upper electrodes 18 will preferably be disposed in a circle with one in the centre, substantially as shown in Fig. 3, but any suitable arrangement may be adopted. These upper electrodes will preferably be suspended separately, so that each may be raised and lowered independently of the others, as exemplified in the case of one electrode in Fig. 3, for a purpose hereinafter more fully described.

The lower electrodes 16 are supplied with current through suitable connections 20 located outside the furnace, and the upper electrodes 18 are supplied with current through the connections 22. These connections 20 and 22 are connected to the terminals, not shown,of an electric circuit, supplied from any suitable source of electricity. While any suitable current, either direct or alternating, may be used, I preferably use an alternating current supplied by a transformer (not shown) of any suitable construction, the primary circuit of which will preferably be provided with means for regulating the voltage delivered by the transformer to the furnace.

Upon the grate 8 I preferably provide electrically conductive means, preferably a. layer of any suitable electrically conductive material in which the lower electrodes 16 are embedded within the furnace. For this purpose I may use granulated coke, the lower portion 21 of the layer being preferably of coarse coke and the upper portion 23 of said layer of relatively fine coke. It will be apparent that the-grate, is not essential, but I prefer to use it as it provides a free space below.

Upon this layer of coke is supported, within what may conveniently be called the reaction chamber of the furnace, the mixture or charge of solid materials that are to take part in the reaction. For the production of aluminum nitride, I prefer to use caicined bauxite, mixed with a suitable proportion of a reducing agent to which will preferably be added a material which will serve to bind the particles of the charge when it is heated. Instead of bauxite any aluminous material could be used, such for example, as the aluminous residue from alunite after the. extraction of the potash therefrom or kaolin or any clay of high alumina content. The amount of silica contained in clays, however, makes them commercially undesirable for use in the process, although it is possible to use them. A suitable binding material is tar or pitch. If pitch is used, it is convena dry mixture. Any suitable reducing agent may be used, but I preferably use 'a carbonaceous material, such as -cokeor low-ash bitumyself to these exact proportions.

minous coal. I

, In order to facilitate the penetration of the nitrogen gas through the mixture, and

permit the necessary contact between the reagents, it is preferable to reduce the ingredients of the charge'to a relatively finely comminuted state. I have found that, if

they are ground to a fineness which will enable about 80% of the -whole charge to assthrough a 100-mesh sieve, this will su ce. After grinding, the'ingredients are thorou hly mixed in any suitable proportion. I have found that a satisfactory mixture will consist of the following proportions: 100 pounds of bauxite; 50 pounds of any good low-ash bituminous coal; and 10 poun s of powdered pitch, but I do not limit I prefer to use pitch instead of makes the mixture heavier andtherefore less permeable to gases. I also preferably make up the charge as a loose mixture, without compressing it, thus minimizing the density and'gaining in permeability to gases. The

degree of porosity of a charge, and of its consequent permeability 'to gases, is in inverse ratio'to its weight per unit'volumne A mixture of finely ound bauxite, coal or coke, and powdere -poured,'weighs only from 40 to 50 pounds per cubic foot, and I have found that a loosely poured dr mixture of these ingredients has a muc greater permeability to gases than any other form of charge known to me.

.It is preferable to separate the charge from the furnace walls or keep it out of contact with the latter, in order among other things to insulate the charge from the walls of the furnace and reduce the loss of heat from the char e by radiation through the furnace walls. Iurthermore, the charge herein usedfor the production of aluminum nitride is electrically non-conductive when cold and must be heated to be rendered conductive. I To the above ends I preferably interpose between the charge and the walls of the furnace a layer of any suitable material cap-- able of withstandin the relatively high temerature towhich t e interior of the furnace is exposed during the'reac'tion, and for this purpose I preferably select a substance that will be relatively conductive when cold, and

. which will therefore act as a resistor when an electric current is passed throu h the same, and thus heat the charge. "ertain carbonaceous substances give good results tar, as tar pitch, when loosely when used for this purpose. I have found invention, however, I may use any suitable substance or'means for this purpose.

Where the charge must be preheated in the furnace to render it self-sustaining, this surrounding layer 26 acts as a supporting means orenvelope for the charge, to support it until it becomes self-sustaining.

It will be apparent that, where the charge is made up of materials that render it electrically conductive when cold or at a normal temperature, the surrounding envelope 26 need not consist of electrically conductive material. Any suitable material or other means that can-withstand the high temperature during the reaction, and which is preferably heat-insulating, may be used.

As-already stated, the charge rests upon the layer of granulated coke in which the lower .electrodes are f embedded, and with which the charge is therefore in electrical contact.

To facilitate the introduction of the charge 24 and its surrounding envelope 26, without their becoming intermixed, I preferably provide suitable separating means, herein exemplified as a cylindrical form 28 having a diameter somewhat less than the interior diameter of the furnace. This form is set up vertically, substantially axially with the furnace, thus leaving an annular space between it and the furnace walls. This annular space will vary somewhat in thickness according to the diameter of the furnace; in a furnace having an interior diameter of seven feet, the cylindrical form may be approximately five feet in diameter, thus leaving an annular space of approximately one foot in thickness between it and the outer Walls of the furnace. The interior'of the form is now filled in with the charge, and the annular space with the granulated coke or other material that is to constitute the supporting envelope. This form may be'made of any suitable material, such as cardboard for example, in which case it will The consumed during the operation, if left in; or it maybe withdrawn as the charge and envelope are filled in u on opposite sides thereof, as when the enve ope and charge are once in place they have no further tendency to mingle.

The furnace is thus filled with the chargeon the inside of the form, and granulated coke on the outside, to the level of the top of the form. Above the top of the form is added a layer of electrically conductive material 30, granulated coke for example, like the layers 21, 23, in which are embedded the lower ends of the carbon electrodes 18 The top coke \layer 30 may, if desired,

be confined to the space within the form, the envelope material running to the top tubes or rods 32 of any suitable material within the form 28 before the charge is introduced, and filling the latter. in around the tubes 32, which should be suitably spaced apart, about 12 inches, for example. These tubes or rods may be made of paper. Wood, or any other suitable material and of any shape in cross-section.

The furnace walls will preferably be provided with a plurality of sight-tube holes 34, placed at different heights and in different angular positions around the furnace.

In the furnace shown, there are four vertical series of these sight-tube holes placed 90 apart around the furnace. A tube extending into the interior of the charge may be inserted. in these sight-tube holes, as shown at 36, by means of which the temperature of the interior maybe read at any time, by either the insertion of a thermo-couple or the use of an optical pyrometer, the choice of the means for read ing temperature being governed by the ranges of temperature to be read. The temperature of practically\ all parts of the charge may thus be ascertained at any time.

After the furnace has been charged as above described, current is thrown on from the transformer. As above stated, the charge of bauxite, coal and pitch, used in the present illustrative instance, does not conduct when it is cold, but the top layer of coke 30, the lower layer of coke 21, 23 and the-annular envelope of coke 26 connecting these upper and lower layers do conduct, so that the circuit is completed between the upper and lower electrodes by the continuous path of coke thus formed. The

first effect of turning on the current is, therefore, to develop heat in the coke forming the top and bottom coke layers 30 and of the volatile components of the pitch and 1 coal will have been driven off, and the fixed carbon' remaining from this distillation bindsthe particles of the charge to each other, so that the whole mass of the\charge is self-sustainin and needs no further support eithenfrom t e outside coke layer or from the tubes'in order to retain its form. Approximately at this point the charge itself begins to conduct the current, so that during the subsequent operation the charge itself serves to establish the circuit between the top and bottom coke layers.

If coring tubes of wood or paper have been used, durin the heating throughout the mass these Wlll begin to distill and decompose before the baking of the charge is completed, but it is found that the charcoal resulting from the use of such tubes holds the position it occupied in the original tube and furnishes a suflicient barrier to prevent the charge from falling into and stopping up the core-holes. After the baking of the charge to a self-sustaining mass is completed, the temperature of the charge continues gradually to rise until the reaction temperature'is reached. Before this te'mperature is reached, the nitrogen will be turned on, sot-hat it may enetrate and pass up through the charge. i n so doing it becomes heated in passing through the coke layers 21, 23 and this contributes to heating the charge. The reaction begins and proceeds very slowly at a temperature of about M00 (1, but its speed rapidly increases as the temperature rises above that point and it proceeds with a rapidity sufficient to make the process commercial at temperatures be tween 1600 and1700 C. The rapidity of the reaction increasesvery rapidly with a rise in the temperature above 1650 C. The conductivity of the charge relative to the conductivity of the" coke envelope also increases very greatly with the rising temperature, and at the reaction temperatures actually used, the major portion of the current in the furnace passes through the charge and develops the heat where it is required to supply that which is absorbed by the reaction, which latter is highly endothermic.

After the charge is brought to the reaction temperature it is necessary to continue to supply it with energy untilenough energy in excess of thatlost by conduction, convection and radiation has been supplied to it,

to convert the major portion of the alumina in the charge into nitride. After this amount of energy has been supplied, any further input of energy ceases to be useful and will result in a further rise of temperature in the charge which, if continued, will destroy the nitride already formed. During the progress of the reaction, which in a.

seven-foot furnace may take from about five toseven hours, the rise of temperature is arrested by the fact that the energy supplied the'completion of the reaction and because.

also above this temperature very rapid volatilization of alumina takes place, and decomposition of the nitride formed begins.

If charcoal-forming coring tubes have been used, the charcoal may or may not remain in place, but if it does it will do no harm because the'charcoal is sufficiently permeable to the gas not to interfere with the entrance nor with the penetration of the charge by the nitrogen.

After the current is turned off the supply of nitrogen will preferably be continued, as

the reaction will not stop when the current is turned off, if there is any unconverted alumina still remaining in-the charge, but

will continue until the temperature of the charge has fallen to a point inthe neighborhoodlofil400 0. Continued introduction of the nitrogen after the current is turned off also "serves to prevent the diffusion of air through the charge, which diffusion might have the effect of oxidizing some of the aluminum nitride already formed; It also helps to cool the charge.

While pure nitrogen could be used in the reaction, this would be expensive, and the use of pure nitrogen is not-necessary. An

atmosphere consisting of approximately 95 to 98% nitrogen, with some carbon dioxide, some carbon monoxide, and a small quantity of free oxygen, can be cheaply made and supplied. This gas is found to be entirely suitable. Ordinary producer gas can also be used to good advantage, but its high carbon dioxide *and carbon monoxide content make it less desirable than an atmosphere richer in nitrogen. Any carbon dioxide present in the gas is reduced to carbon monoxide, by

the carbon of the coke in the bottom of the furnace and by the carbon in the charge, but

as this conversion is an'endothermic reaction, it takes place at the expense of electrical energy, and. for this reason it is desirable used shall be as'low as practicable.

that the carbon dioxide content of the Agas y oxygen in the gas turnsto carbon dioxide with the carbon at the bottom of the furnace,

and afterwards is reduced to carbon monoxide at the expense of electrical energy.

While the presence of carbon monoxide to a V .reasonable amount does not interfere seriously with the reaction, yet when this carbon monoxide content of the gas rises to approximately 60% or above, it does begin to inter-' used.

It will be apparent that, whenthe furnace charge is brought to reaction temperature,

the total quantity of energy passing through-v the furnace divides in its passage between the charge and the coke envelope. The portion of the energy which passes through the envelopeserves to supply the heat lost by radiation and conduction through the furnace walls, permitting all the energy which is developed within the charge itself to be usefull a plied in causing the reaction to proceed he carbonaceous envelope surrounding the charge, therefore, serves this useful purpose'in addition to those already enumerated, 4

At the temperature necessary to maintain within the furnace for carrying out the reaction, the interior walls of the furnace reach a temperature at which they themselves become conductors of the electric current. The result of this is that a portion of the current may leak wastefully around the charge along the interior surface of the walls of the furnace, from the'top coke layer to thebottom coke layer. This both wastes energy and contributes to the damage of the furnace walls. Meansare accordingly herein provided to overcome this, said means being herein exemplified, for example, by two water coils 38,38, see Fig. 2, embedded in the wall of the furnace, adjacent its inner surface, one of said coils being located just below the upper layer ofvcoke 30, and the other just above the lower layer of coke 23. Through suitable connections, not shown, a circulation of cold water from any suitable source of supply, not shown, may be maintained through these coils, whereby the walls of the furnace, for a sufficient distance inward from their inner surface, will be maintained at a sufiiciently low temperature where said coils are located, to prevent leakage of electric current around the charge,

along the interior surface of the furnace.

' The carbonaceous envelope protects the charge during the reaction, so that the furnace may be operated without a top, as the charge is protected on all sides by the carbonaceous shield which prevents air from filtering into it and/oxidizing it.

In startin a furnace of the character de scribed, particularly if it be a large one, certain precautions are found to be desirable in practice. Carbon or coke has a much higher electrical resistance when cold than when hot; consequently, when the current is first applied, if any portion of the envelope happens to be of less resistance than the balance thereof, more current asses through that portion than through t 1e portions of higher resistance, and heating proceeds more rapidly at that point than at the other points. As the temperature in these zones of less resistance rises, the resistance tends to diminish still more and the quantity of current admitted, therefore becomes still greater, so

that the effect is cumulative. The tendency is, therefore, for the envelope to heat up at one point faster than at other points, and this effect is also cumulative. For this reason it is desirable that the initial heating shall proceed slowly, so that no point in the furnace shall be supplied with energy more rapidly than it can be conducted to the neighboring colder portions to equalize temperatures. The unlform heating of the envelope can be facilitated by various means. In practice it has been found that this may be accomplished, for example, by dividing the coke layer at the top of the furnace into sections, electrically insulated from each other, and each one supplied with current by a separate electrode.

as by dividing the top coke layer into sectorsby boards or partitions. The entire annular envelope may also be divided in this way, so as to confine the current to the sector in which it starts, but in practice this has been found to be unnecessary. The amount of current entering any sector can be controlled inany one of several ways, as

will be clear to those skilled in the art, for example by a variable reactance or resistance in the circuit of each electrode, but preferably by varying the pressure of the electrode on the coke which it enters. The electrical resistance of a mass of loose coke is very greatly reduced by increasing the contact pressure on it, and 1n practice it has been found desirable, as already stated, to suspend the upper electrodes separately, with means to raise or lowerthem independently so as to be able to increase or decrease the intimacy of contact between the individual electrodes and the coke. Thus, if it is found in starting that one electrode is carrying more current than the others, this current" This sectionalizing can be readilyeflected by any suitable means,

electrode, and conversely, any electrode which is carrying too little current can be lowered to raise the amount of current it carries. In practice, the electrodes will referably bethus adjusted separately until all conduct about the same amount of current,

tion by the oxygen of the air. After the temperature of thecharge has fallen to a point below 800 to 900 C., this oxidation of the nitride in. the charge will no longer take place, and the finished charge can then be removed from the furnace in any suitable manner and by any suitable means.

From what has been said with regard to the liabilitv of the charge oxidizing at the reaction temperature, should oxygen be admitted, it will be apparent that in order to be successful the reaction must be conducted in a reducing atmosphere. This is assured in my process by the presence of the heated carbon in the coke layers 21, 23, which combines with any oxygen that may enter the furnace to form carbon dioxide, which is afterwards reduced to carbon monoxide, and also to the presence of large quantities of the latter gas, resulting from the reaction.

The charge may be putinto the furnace in dry, powdered form, as above described,

or it may be previously mixed with the tar or pitch.at a temperature high enough to render the binding material thoroughly fluid, and put into the furnace in a plastic or semi-plastic condition. It will also be apparent that the charge could be heated, in a suitable form, for example, to render it self-sustaining before placing it in the furnace, and the coring if used, may also be effected before the charge is placed in the furnace.

From the above description those skilled in the art will readily recognize the advantages possessed by my invention.

Thus, uniform heating of the charge and consequent uniform. electrical conductivity throughout all parts of the latter is assured by my invention so long as an endothermic reaction is roceeding, on condition that the materials or the reaction be everywhere present in the charge in quantities and under conditions to enable the reaction to roceed freelyvin all parts of the charge. his condition my invention fulfills owing to the intimate and -substantially uniform inter mixture of the ingredients ofthe charge throughout the entire mass of the latter, andthe hlgh" degree of porosity of the charge throughout, whereby intimate and so far as practicable uniform contact is assured between the solid and gaseous bodies used in the reaction, throughoutthe entire mass of the charge, and fresh gas can always permeate any and all parts of the latter to take the place of that absorbed by the reaction. The heat necessary for the reaction will thus be developed throughout the entire charge wherever it is required and in suitable quantity continuously to supply that absorbed by the reaction.

So far as practicable, uniform heating of the charge throughout is thus assured and overheating thereof during the reaction is precluded provided that therate of input of electrical energy is kept within certain limits, readily determined by experiment;

this rate being substantially equal to the sum of the heat absorbed by the reaction,

plus theunavoidable heat losses, the temperature being thus maintained within the desired limits.

Where the charge is not substantially uniformly heated, the electric current owing to the greater conductivity of the hotter portions of the charge, isliable to concentrate at said hotter portions. The temperature of the hotter portions of the charge is thus liable to rise to the fusion point of the mixture, the resulting fused masses cutting off the supply of gas from adjacent parts of the charge, thus materially curtailing if not wholly preventing the reaction at those parts. The uniform heating of the charge in accordance with my invention precludes this and ensures that the reaction will take place practically uniformly in all parts of the'charge, thus ensuring a very high production of the product which it is sought to obtain.

Other advantages secured by my inven-f vtion, in addition tothose herein specifically pointed out, will appearto those skilled in the art.

It will be understood that, while-the in-- vention is herein described as embodiedin the' details illustrated, the invention is not to be considered as circumscribed by or limited to these details or any of them, but that said details may be variously modified within the true scope of the invention which is definitely set forth by the claims. It will be understood also that it is not indispensa blethat all the features of the invention be used conjointly, since they may be used to advantage separately in various combinations and sub-combinations, as defined in i the subjoined claims.

The process herein disclosed is claimed in my companion case of even date, Serial No. 324,764.

Claims:

1. In apparatus of the class described, in combination, a reaction chamber enclosed laterally "by a wall; a grate adjacent the bottom of said reaction chamber; a plurality of pipes extending through said wall and opening into the space beneath said grate and connected to a suitable gas supply; a lower layer of coke above said grate and supporting a charge within said reaction chamber; an upper layer of coke supported by said charge; a lateral layer of coke surrounding and supporting said charge laterally and interposed between the latter and said wall and connecting said upper and lower layers; a plurality of lower electrodes having their inner ends embedded in said lower coke layer; a plurality of upper electrodes having their inner ends in contact with said upper coke layer; and electrical connections connecting said electrodes with a suitable source of electric current.

2. In apparatus of the class described,in' combination, a reaction chamber enclosed laterally by .a wall; a grate adjacent the bottom of said reaction chamber; gas conducttrical connections connecting said electrodes laterally bya wall; a grate adjacent the bottom of said reaction chamber; gas conductthe' space beneath said grate and connected with a suitable source of electric current. 3. In apparatus of the class described, in

combination, a reaction chamber enclosed 'ing means extending through said wall into 1 to a'suitable gas supply; layers of coke above I said grate and having between them a charge in said reaction chamber; a lateral layer of coke" surrounding and supporting said charge and interposed between the latter and said wall and connecting said first-named coke layers; a plurality of electrodes in electrical contact with said first-named layers; electrical connections connecting said electrodes with a suitable source of electric current; and means to vary the contact pressure between one or more of said electrodes and the coke.

4. In apparatus of the class described, in

combination, a reaction chamber enclosed laterally by a wall; a grate adjacent the bottom of said reaction chamber; gas conducting means extending through said wall into the space beneath said grate and connected to a suitable gas supply; layers of electrically conductive material above said grate and having between them a charge in said :reaction chamber; a lateral layer'of electrically conductive material surrounding and supporting said charge and interposed between the latter .and said wall and connecting said first-named layersof electrically conductive material; a plurality of electrodes in electrical contact with said first-named layers of electrically conductive material; electrical connections connecting saidelectrodes with a suitable source of electric current; and means to vary the contact pressure between one or more of said electrodes and the electrically conductive material.

5. In apparatus of the class described, in combination, a reaction chamber containing a charge; means to conduct a gas into said reaction chamber below said charge; a layer of electrically conductive material supporting said charge; a layer of electrically conductive material supported by said charge; a plurality of electrodes in electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections connecting said electrodes with a suitable source of electric current.

6. In apparatus of the class described, in combination, a reaction chamber containing a charge that is electrically non-conductive at normal temperatures; means to conduct gas into said reaction chamber below said charge, so that it may permeate the latter; a layer of electrically conductive material supporting said charge; a layer of electrically conductive material supported by said charge; a plurality of electrodes in electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections connecting said electrodes with a suitable source of electric current, where by electric current will first pass through said three layers of electrically conductive material to heat them and thereby to heat the charge and render it electrically conductive, and will then pass through said charge and generate throughout the latter the heat necessary for the reaction.

7 In apparatus of the class described, in combination, a reaction chamber containing a cored charge comprising the solid materials to take art in the reaction, relatively finely divided and thoroughly intermixed, said charge being electricall non-conductive until heated; means 'to condiict the gas that is totake part in the reaction into said reaction chamber below said charge, so that it may permeate the latter; a layer of electrically conductive material supporting said charge; a layer of electrically'conductive material supported by said charge; a plurality of electrodes in electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections connecting said electrodes with a suitable source of electric current, whereby electric current will first pass through said three layers of electrically conductive material to heat them and thereby to heat the charge and render it electrically conductive, and will then pass through said charge andgenerate throughout the latter the heat necessary for the reaction.

8. In apparatus of the class described, in combination, a reaction chamber containing a charge comprising the solid materials to take part in the reaction and a binding material that will bind the particles of said materials together'when it is heated, all of said materials being relatively finely divided and thoroughly intermixed; said charge being electricallyv non'- conductive until heated; means to conduct the gas that is to take part in the reaction into said reaction chamber below said charge, so that it may permeate the latter; a layer'of electrically conductive material supporting said charge; a layer of electrically conductive material supported by said charge; a plurality of electrodes in electrical contact ,with said layers; a lateral layer of electrically conductive material surroundingsaid charge and electrically connecting said first-named two layers; and electrical connections connecting said electrodes with a suitable source of electric current, whereby electric current will first pass through said three layers of electrically conductive material to heat them and thereby to heat the charge and render it selfsustaining and electrically conductive, and will then pass through said charge and generate throughout the latter the heat necessary for the reaction.

9'. In apparatus of the class described, in combination, a reaction chamber containing a cored charge comprising the solid materials to take part in the reaction and a binding material that will bind the particles of said materials together when it is heated, all of said materials being relatively finely divided and thoroughly intermixed, said charge being electrically non-conductive until heated; means to conduct the gas that is to take part in the reaction into said reaction chamber below said charge, so that it may permeate the latter; a layer of electrically conductive material supporting aid charge; a layer of electrically conductive material supported by said charge; a plurality. of electrodes in. electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections connecting said elec trodes with a suitable source of electric current, whereby electric current will-first pass containing a charge comprising a suitable aluminous material, a suitable carbonaceous material, and a bindlng material that will bind the particles of said charge together when it is heated, in suitable proportions, all of the materials of said charge being relatively finely divided and thoroughly inter- .mixed, said charge being electrically nonconductive until heated; means to conduct a nitrogen-containing gas into said reaction chamber below said charge, so that itmay permeate the latter; a layer of electrically conductive material supporting saidchar'ge; a layer of electrically conductive material supported by said charge; a plurality of electrodes in electrical contact with said layers; a lateral'layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers and-electrical connections connecting said electrodes with a suitable source of electric current, whereby electric current will first pass through said three layers ofelectrically conductive material to heat them, and thereby to heat the charge and render it self-sustaining and electrically conductive, and will then pass through said charge and generate throughout the latter the heat necessary for the reaction.

11. In apparatus for making aluminum nitride, in combination, a reaction chamber containing a cored charge comprising a suitable aluminous materlal, a suitable carbonaceous material, and a binding material that, will bind the particles of said charge together when it is heated, in suitable propors tions, all'of the materials of said charge being relatively finely divided and thoroughly intermixed, said charge being electrically non-conductive untilheated; means to conduct .a nitrogen-containing as into said reaction chamber below said 0 arge, so that it may permeate the latter; a layer of electrically conductive material supporting said charge; a layer of electrically conductive material supported by said charge; a plurality of electrodes in electrical contact with said layer; a lateral layer'of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections con:

necting said electrodes with a suitable source of electric current, whereby electric current about 50 pounds of bituminous coal, and

about 10"pounds of powdered pitch, all of the materials of said charge being relatively finely divided and thoroughly intermixed,

said charge being electrically non-conductive until heated; means to conduct a nitro gen-containing gas into said reaction cham ber below said charge, so that it may permeate the latter; a layer of electricall conductive material supporting said cha ge; a layer of electrically conductive material supportedby said charge; a plurality of electrodes in electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting first-namedtwo layers; and electrical connections connecting said electrodes with a suitable source of electric current,whereby electric current will first pass through said three layers of electrically conductive material to heat them and thereby to heat the charge and render it selfsustaining and electrically conductive, and will then pass through said charge and generate throughout the latter the heat necessary for the reaction.

.13. In apparatus for makin aluminum nitride, in combination, a reaction chamber containing a cored charge, comprising bauxite, bituminous coal, and powdered pitch in the proportions of about 100 pounds of bauxite, about 50 pounds of bituminous coal, and about 10 pounds of powdered pitch, all of the materials of said charge being relatively finely divided andthoroughly intermixed, said charge being electrically nonconductive until heated; means to conduct a nitro en-containing gas into said reaction cham er below said charge, so that it may permeate the latter; a layer of electrically conductive material supporting said charge; a layer of electricallyzconductive material supported by said charge; a plurality of electrodes in electrical contact with said layers; a lateral layer of electrically conductive material surrounding said charge and electrically connecting said first-named two layers; and electrical connections connecting said electrodes with a suitable source self-sustaining and/electricall of electric current, whereby electric current will first pass through said three layers of electrically conductive material to heat them and thereby to heat the charge and render it conductive, and will then pass through sald charge and generate throughout the latter the heat necessary for the reaction.

14. An apparatus of the classdescribed comprising a chamber having electrodes at either end thereof and a conductive pervious lining for said chamber interposed between a separating element for laterally supporting said lining. a

17. In apparatus of the class described, in combination, a reaction chamber containing a charge; an electrical resistor enclosing said charge; and electrical connections connecting said resistor with a suitable source of electric current.

18. In apparatus of the class described, an

electrical resistor; electrical connections connectlng said reslstoradapted to receive a charge in proximity thereto to a suitable source of electric current, and means to equalize the distribution of the electric current in said resistor.

19'. An apparatus of the class described comprising a chamber having aplurality of electrodes at either end thereof, conducting layers in which said electrodes are received and between which a charge is interposed and means dividing one of said layers between electrodes.

20. An apparatus of the class described comprising a chamber having a plurality of electrodes at either end thereof, partitions between electrodes of one set and a layer of carbon lumps between said partitions forming a sectionalized conducting layer adjacent the charge;

21. An apparatus of the class described comprising a chamberhaving refractory walls and electrodes at either end, conductive means between said electrodes including a lateral lining for the walls providing an interior space for the reception of a charge and means for cooling the walls to prevent conduction of current therealong.

22. In apparatus of the class described in combination, a reaction chamber containing a charge; a supporting layer of material for said charge; and means to prevent the matecombination, a reaction chamber containing a charge; supporting means for the charge; and removable separating means for said charge and supporting means.

26. In apparatus for practising chemical reactions between solid and gaseous bodies, in combination, a reaction chamber; adapted to receive a loosely poured charge, said charge comprising the solid bodies to take part in the reaction and being electrically non-conductive until heated; means to heat said charge; a plurality of electrodes be tween which said charge is adapted to form a conductive path when heated; electrical connections connecting said electrodes with a suitable source of electric current; means to core said charge; and means to conduct the gaseous body to take part in the reaction into said reaction chamber.

27. In apparatus for practising chemical reactions between solid and gaseous bodies, in combination, a reaction chamber; adapted to receive a loosely poured charge, comprising the solid bodies to take part in the reaction and being electrically non-conductive until heated; an electrical resistor to heat said charge; 'a plurality of electrodes be tween which said charge is adapted to form a conductive path when heated; means to core said charge; means to conduct the gaseous body to take part in the reaction into said reaction chamber; and electrical connections connecting said electrodes and said resistor with a suitable source of electric current.

28. In apparatus for practising chemical -reactions betweensolid and gaseous bodies,

with a suitable source of electric current.

In apparatus for making aluminum nltride, 1n combination, a reaction chamber;

" adapted to receive a loosely poured charge comprising a mixture 'of a suitable proportion of bauxite, a suitable proportion of coke or coal, and a suitable proportion-of pitch, all reduced to a relatively finely comminuted state; an. electrical resistor to heat the charge; a plurality of. electrodes between which said charge is adapted to form a conductive path when heated; electrical connections connecting said resistor and said electrodes with a suitable source of electric current; means to core said charge; and means to conduct a nitrogencontaining gas into said reaction chamber.

30.-In apparatus for making aluminum nitride, in combination, a reaction chamber; adapted to receive a loosely poured charge comprising a mixture of bauxite, coal and pitch, all reduced to a relatively finely coinminuted state and in the. proportions of about 100 pounds ofbauxite, about 50 pounds of coal, and about 10 pounds of powdered pitch; an electrical resistor to heat the charge; means to produce a reducing atmosphere in said reaction chamber; a plurality of electrodes between which said charge is adapted to form a conductive path when heated; electrical connections connecting said resistor and said electrodes with a suitable source of electric current; means to core said charge; and means to conduct a nitrogen-containing gas into said reaction chamber. a

In testimony'whereof, I have signed my name to this specification. s

WILLIAM HOOPES. 

